The UK is thought to be preparing to suspend parts of the Brexit deal for Northern Ireland - known as the protocol.
This was designed to prevent checks along the border between Northern Ireland (in the UK) and the Republic of Ireland (in the EU), following Brexit.
But since it came into force at the start of 2021, the protocol has prompted disagreements between the UK and EU because it has disrupted trade between Great Britain and Northern Ireland.
What is the Northern Ireland Protocol?
During Brexit negotiations, all sides agreed that protecting the 1998 Northern Ireland peace deal (the Good Friday agreement) was an absolute priority.
That meant keeping the land border open and avoiding new infrastructure such as cameras and border posts.
This was easy to do when both Ireland and Northern Ireland were part of the EU. Both sides automatically shared the same EU rules on trade and no checks were needed on goods travelling between them.
However, a new arrangement was needed after Brexit.
The EU requires many goods - such as milk and eggs - to be inspected when they arrive from non-EU countries, while some products, such as chilled meats, aren't allowed to enter at all.
Under the protocol it was agreed that Northern Ireland would continue to follow EU rules on product standards (part of the EU's single market rules) to prevent checks along the border. Checks would instead take place on goods entering Northern Ireland from England, Scotland or Wales.
Inspections take place at Northern Ireland ports, and customs documents have to be filled in.
This has prompted criticism that a new border has effectively been created in the Irish Sea.
But the full effect of the protocol has been limited so far, by the suspension of checks (known as "grace periods'") in certain areas.
What changes are the UK government calling for?
Boris Johnson signed up to the agreement in 2019 and promised during that year's general election campaign that it would not create any checks on goods moving between Great Britain and Northern Ireland.
However, the government now says the protocol represented a huge compromise by the UK, and it has accused the EU of applying it too rigidly.
Brexit Minister Lord Frost has submitted proposals to change the protocol. They include getting rid of customs checks between Great Britain and Northern Ireland, and relying on businesses to be honest about what they are doing.
He has proposed a new system in which goods would be able to circulate freely in Northern Ireland if they conform to either EU or UK regulations. At the moment they have to meet EU standards.
The government also wants to remove the role the European Commission and the European Court of Justice have in overseeing how the protocol works.
What is Article 16?
If the UK does not secure changes to the protocol, it could decide to trigger Article 16.
This allows either side to suspend any part of the agreement that causes "economic, societal or environmental difficulties".
Lord Frost told the Conservative Party conference that triggering Article 16, may be "the only way" forward, although the government says it won't trigger it before holding talks with Brussels.
A UK decision to use Article 16 could prompt the EU to respond with measures which would impose tariffs (or import taxes) on aspects of trade between the two sides.
The EU has warned that any such move by the UK would be "serious for Northern Ireland as it would lead to instability and unpredictability".
What has the EU proposed?
The EU has said a renegotiation of the text of the Protocol is out of the question.
But it has set out proposals that it says would lead to an 80% reduction in checks on food products arriving in Northern Ireland, as well as halving the amount of paperwork involved.
For example, a lorry arriving from Great Britain carrying a load of different farmed food products would only need a single certificate - instead of needing a different one for each product.
The EU is also proposing a reduction in the customs information firms need to provide and says it intends to pass legislation to allow the trade in medicines between Great Britain and Northern Ireland to continue.
And rules that would have prevented chilled meats such as Cumberland sausages being sent across the Irish Sea would also be relaxed.
But in return, the EU wants extra safeguards to prevent products from Great Britain crossing into the Republic of Ireland - as well as access to UK data showing real-time trade flows.
European Commission Vice President Maros Šefčovič said he hopes the proposals will form the basis for intensive talks with the UK. Lord Frost has indicated that he is willing to discuss them seriously.
What about security concerns?
As well as problems with trade, there are also political and security concerns in Northern Ireland.
Checks were temporarily suspended at the start of the year over what were described as "sinister" threats to some border staff checking goods.
Unionists are strongly opposed to the checks because they don't want Northern Ireland to be treated differently to the rest of the UK.
There have been a series of demonstrations and protests against any kind of border in the Irish Sea.